1. Field of the Invention
This invention relates to a liquid crystal display, and more particularly to a driving apparatus and method for a liquid crystal display wherein a picture may be inspected by a specific image signal when an image signal is not applied.
2. Description of the Related Art
Generally, a liquid crystal display (LCD) of an active matrix driving system uses thin film transistors (TFT's) as switching devices to display a natural moving picture. Because this type of LCD can have a smaller size than a Brown tube, they have been widely used in monitors for personal or notebook computers as well as office automation equipment such as a copy machine, etc. and portable equipment such as a cellular phone or a pager, etc.
The active matrix LCD displays a picture corresponding to video signals, such as television signals, on a picture element matrix or pixel matrix having liquid crystal cells arranged at intersections between gate lines and data lines. The thin film transistor is provided at each intersection between the gate lines and the data lines thereby switching a data signal to be transmitted into the liquid crystal cell in response to a scanning signal (or gate pulse) from the gate line.
LCDs may display either NTSC signals and/or PAL signals.
Generally, if an NTSC signal (i.e., 525 vertical lines) is input, a horizontal resolution of the LCD is expressed in accordance with a number of sampled data while a vertical resolution thereof is expressed by a 234 line de-interlace scheme. On the other hand, if a PAL signal (i.e., 625 vertical lines) is input, the horizontal resolution of the LCD is expressed in accordance with a number of sampled data while a vertical resolution thereof is modified using a processing system to produce a NTSC signal in which one line is removed for each six vertical lines which results in 521 lines.
Referring to FIG. 1, a conventional LCD driving apparatus includes a liquid crystal display panel 30 having liquid crystal cells arranged in a matrix a gate driver 34 for driving gate lines GL of the liquid crystal display panel 30, and a data driver 32 for driving data lines DL of the liquid crystal display panel 30. The LCD driving apparatus also includes an image signal processor 10 for extracting a complex synchronizing signal Csync and red, green and blue image signals R_Video, G_Video and B_Video from an NTSC complex image signal. The image signal processor also functions to apply the red, green and blue image signals R_Video, G_Video and B_Video to the data driver 32 and output the complex synchronizing signal Csync. In addition, the LCD driving apparatus has a controller 20 for receiving the complex synchronizing signal Csync from the image signal processor 10 to generate a data control signal DCS for controlling the data driver 32 and a gate control signal GCS for controlling the gate driver 34. The controller 20 also functions to apply the DCS and the GCS to the data driver 32 and the gate driver 34, respectively.
The liquid crystal display panel 30 includes liquid crystal cells arranged in a matrix and thin film transistors TFT provided at intersections between the gate lines GL and the data lines DL which connect to the liquid crystal cells.
The thin film transistor TFT is turned on when a scanning signal, such as a gate high voltage VGH from the gate line GL is applied, thereby applying a pixel signal from the data line DL to the liquid crystal cell. On the other hand, the thin film transistor TFT is turned off when a gate low voltage VGL is applied from the gate line GL, thereby maintaining a pixel signal charged in the liquid crystal cell.
The liquid crystal cell can be modelled as a liquid crystal capacitor LC and includes a pixel electrode connected to a common electrode and a thin film transistor TFT opposed to the electrodes with a liquid crystal disposed there between. Further, the liquid crystal cell includes a storage capacitor Cst for stably maintaining the charged pixel signal until the next pixel is charged. The storage capacitor Cst is provided between a pre-stage gate line and the pixel electrode. Such a liquid crystal cell varies an alignment state of the liquid crystal having a dielectric anisotropy in response to the pixel signal charged via the thin film transistor TFT to control a light transmittance, thereby implementing a gray scale level.
The image signal processor 10 converts the complex image signal NTSC supplied from the exterior thereof into red, green and blue image signals R_Video, G_Video and B_Video such that the signals are suitable for driving the liquid crystal display panel 30. The image signal processor 10 also applies the signals to the data driver 32, and extracts the complex synchronizing signal Csync from the complex image signal NTSC and applies the complex synchronizing signal Csync to the timing controller 20.
The timing controller 20 generates a horizontal synchronizing signal Hsync, a vertical synchronizing signal Vsync and a dot clock Dclk using the complex synchronizing signal Csync from the image signal processor 10 and applies both signals to the data driver 32. Further, the timing controller 20 generates a data control signal DCS for controlling the drive timing of the data driver 32 and applies the data control signal DCS to the data driver. The timing controller 20 also generates a gate control signal GCS for controlling the drive timing of the gate driver 34 and applies the gate control signal GCS to the gate driver 34 with the aid of the horizontal synchronizing signal Hsync, the vertical synchronizing signal Vsync and the dot clock Dclk.
The gate driver 34 sequentially applies the gate high voltage VGH to the gate lines GL in response to gate control signals GSP, GSC and GOE from the timing controller 20. Thus, the gate driver 34 allows the thin film transistors TFT connected to the gate lines GL to be driven for each gate line.
More specifically, the gate driver 34 shifts a gate start pulse GSP in response to a gate shift pulse GSC to generate a shift pulse. Further, the gate driver 34 applies the gate high voltage VGH to the corresponding gate line GL every horizontal period H1, H2, . . . in response to the shift pulse. Here, the gate driver 34 applies the gate high voltage VGH only in an enable period in response to a gate output enable signal GOE. On the other hand, the gate driver 34 applies the gate low voltage VGL in the remaining period when the gate high voltage VGH is not applied to the gate lines GL.
The data driver 32 applies pixel data signals for each line to the data lines DL every horizontal period H1, H2, . . . in response to the horizontal synchronizing signal Hsync, the vertical synchronizing signal Vsync, the dot clock Dclk and data control signals SSP, SSC and SOE from the timing controller 20 as shown in FIG. 2. Particularly, the data driver 32 converts the red, green and blue image signals R_Video, G_Video and B_Video from the image signal processor 10 into analog data and applies the image signals to the data lines DL.
More specifically, the data driver 32 shifts a source start pulse SSP from the timing controller 20 in response to a source shift clock SSC to generate a sampling signal. Then, the data driver 32 sequentially inputs the red, green and blue image signals R_Video, G_Video and B_Video for a certain unit in response to the sampling signal thereby latching the image signals. Further, the data driver 32 applies the latched analog data for one line to the data lines DL.
Meanwhile, a panel aging process for displaying a specific image signal on the completed LCD is carried out during a fabrication process of the LCD. During the panel aging process, as shown in FIG. 2, the data driver 32 is supplied with the red, green and blue image signals R_Video, G_Video and B_Video and the data control signals from the timing controller 20. Thus, the liquid crystal display panel 30 displays a picture corresponding to the red, green and blue image signals R_Video, G_Video and B_Video.
However, if the red, green and blue image signals R_Video, G_Video and B_Video are not applied to the data driver 32 during the panel aging process, then a black screen only is displayed on the liquid crystal display panel 30 because each of the red, green and blue image signals R_Video, G_Video and B_Video is set to a ground level. Therefore, the conventional LCD driving apparatus has a problem because it is impossible to make a picture inspection for the liquid crystal display panel 30 when the red, green and blue image signals R_Video, G_Video and B_Video are not applied to the data driver 32. Furthermore, the conventional LCD driving apparatus has a problem in that, since it is necessary to apply the red, green and blue image signals R_Video, G_Video and B_Video to the LCD during the panel aging process, it is impossible to detect whether or not the red, green and blue image signals R_Video, G_Video and B_Video are input. As a result, it becomes difficult to set panel aging equipment.